Ultraviolet-cutoff materials have hitherto found expanded applications as an additive to food packaging materials for avoiding degradation of oils, furniture-protective sheets for avoiding discoloration and coloration, sheets for vinyl houses, foundations for preventing a sunburn or skin cancer, ultraviolet-cutoffs fibers, paints stabilized against ultraviolet light, ultraviolet-cutoff glass, papers, and building materials and the like. Basically, the material capable of cutting off ultraviolet light absorbs ultraviolet energy independently of whether it is an organic material or an inorganic material. Therefore, absorption of the ultraviolet energy causes a change in the material, per se, capable of cutting off ultraviolet light or results in release of active oxygen or electrons having a capability of oxidizing an object which comes into contact with the material capable of cutting off ultraviolet light. In many cases, this property becomes a demerit which surpasses the merit provided by the ultraviolet-cutoff effect. Specifically, in an attempt to attain ultraviolet-cutoff effect by adding the material capable of cutting off ultraviolet light to a plastic film, the film per se is photo-deteriorated, deteriorating the durability of the film. Cosmetics with ultraviolet-cutoff effect being imparted thereto has a fear of degrading and denaturing an organic material as a dispersing medium or otherwise photo-deteriorating the skin per se. In the case of an organic ultraviolet-cutoff material, the ultraviolet-cutoff material per se is converted to a different material, resulting in loss of ultraviolet-cutoff activity. Therefore, the ultraviolet-cutoff effect cannot be permanent. On the other hand, in the case of an inorganic ultraviolet-cutoff material, an attempt has been made to coat the surface of the material with an inactive material, such as SiOhd 2 or Al.sub.2 O.sub.3, to inhibit the photocatalytic activity (for example, Japanese Patent No. 1934945).
In the ultraviolet-cutoff material, however, the percentage hiding should be high in order to increase the cutoff effect, and, at the same time, the ultraviolet-cutoff material should be highly permeable to visible light. Therefore, the particle diameter of the inorganic ultraviolet-cutoff material is so small that the cohesive force is high making it impossible to homogeneously disperse the particles. The agglomeration and heterogeneous dispersion lower the cutoff effect and remarkably deteriorates the appearance. For example, titanium oxide for cosmetic applications, coloration inherent in titanium oxide occurs, which is causative of a deterioration in value as cosmetics.
In order to improve the dispersibility, an attempt has been made to bear a flaky clay mineral on the surface thereof (for example, Japanese Patent Application Laid-Open Gazette Nos. 87141/1997 and 59129/1997) or to intercalate the flaky clay mineral. It is a matter of course that, in the material, capable of cutting off ultraviolet light, bearing thereon titanium oxide or hydrated titanium oxide, the titanium oxide or hydrated titanium oxide is exposed on the surface of the ultraviolet-cutoff material. Also in the case of the material, capable of cutting off ultraviolet light, containing titanium oxide or hydrated titanium oxide incorporated by intercalation into between layers based on the principle of ion exchange, exposure of titanium oxide or hydrated titanium oxide coordinated on the outermost surface is unavoidable, and the percentage exposure of titanium oxide or hydrated titanium oxide coordinated on the outermost surface increases with enhancing the degree of dispersion due to a reduction in diameter of fine particles and a reduction in layer thickness.
That is, at the present time, a problem of agglomeration of titanium oxide or hydrated titanium oxide and a problem of exposure of titanium oxide or hydrated titanium oxide could not have been simultaneously solved.
In order to avoid photo-deterioration of the organic substrate by the UV-cutoff material, it is necessary to avoid contact of titanium oxide or the like with the organic substrate. Intercalation of a metal oxide into the clay mineral as means for this purpose is based on the principle of ion exchange. Therefore, a titanium oxide precursor is coordinated on the bottom face which is located on the outermost position of the clay mineral sheet, making it impossible to avoid exposure of Ti0.sub.2. Further, a reduction in layer thickness of the clay mineral and metal oxide or a reduction in diameter of fine particles increase the percentage exposure.
Furthermore, the titanium oxide precursor, upon heating, is strongly bonded to the clay mineral sheet, inhibiting swelling and dispersion as properties of the clay mineral, which makes it impossible to reduce the layer thickness and to reduce the diameter of fine particles.
Likewise, a prior art method, wherein a hydrated titanium oxide sol is hydrolyzed to deposit titanium oxide on the surface of flaky particles of the clay mineral, suffers from this drawback (for example, Japanese Patent Application Laid-Open Gazette Nos. 87141/1997 and 59129/1997).
Accordingly, an object of this invention is to provide an ultraviolet-cutoff material that can make it impossible for the photocatalytic activity, in a material having both ultraviolet-cutoff activity and photocatalytic activity, to be developed and can develop only the ultraviolet-cutoff activity without photo-deterioration of a borne/dispersed organic substrate, and to provide a process for preparing the same.